Uranium is a naturally occurring element with an average concentration of 2.8 parts per million in the Earth’s crust. Traces of it occur almost everywhere. It is more abundant than gold, silver or mercury, about the same as tin, and slightly less abundant than cobalt, lead or molybdenum. Vast amounts of uranium also occur in the world’s oceans, but in very low concentrations.

Uranium mines operate in some twenty countries, though 55% of world production comes from just ten mines in six countries, these six providing 85% of the world’s mined uranium (Fig. 6.1). Most of the uranium ore deposits at present supporting these mines have average grades in excess of 0.10% of uranium — that is, greater than 1000 parts per million. In the first phase of uranium mining to the 1960s, this would have been seen as a respectable grade, but today some Canadian mines have huge amounts of ore up to 20% U average grade. Other mines, however, can operate successfully with very low grade ores, down to about 0.02% U.

Some uranium is also recovered as a by-product with copper, as at Olympic Dam mine in Australia, or as a by-product from the treatment of other ores, such as the gold-bearing ores of South Africa, or from phosphate deposits such as in

Morocco and Florida. In these cases the concentration of uranium may be as low as a tenth of that in orebodies mined primarily for their uranium content. An orebody is defined as a mineral deposit from which the mineral may be recovered at a cost that is economically viable given the current market conditions. Where a deposit holds a significant concentration of two or more valuable minerals then the cost of recovering each individual mineral is reduced as certain mining and treatment requirements can be shared. In this case, lower concentrations of uranium than usual can be recovered at a competitive cost.

Generally speaking, uranium mining is no different from other kinds of mining unless the ore is very high grade. In this case special mining techniques such as dust suppression, and in extreme cases remote handling techniques, are employed to limit worker radiation exposure and to ensure the safety of the environment and general public.

Searching for uranium is in some ways easier than for other mineral resources because the radiation signature of uranium’s decay products allows deposits to be identified and mapped from the air.

Thorium is a possible alternative source of nuclear fuel, but the technology for using this is not established. Thorium requires conversion to a fissile isotope of uranium actually in a nuclear reactor (see Chapter 9) . However, supplies of thorium are abundant, and the element currently has no commercial value. Accordingly, the amount of resource is estimated rather than directly measured as with uranium. Thorium is reported to be about three times as abundant in the Earth’s crust as uranium. The 2009 IAEA-NEA ‘Red Book’ lists 3.6 million tonnes of known and estimated resources as reported, but points out that this excludes data from much of the world, and estimates about 6 million tonnes overall. Making normal assumptions regarding how it might be used, this represents a far greater energy source than the same amount of uranium used in today’s reactors, but about the same if fast neutron reactors are envisaged.